Re: application of KNN code to US zipcode searches?

Mark Stosberg <mark(at)summersault(dot)com> writes:
> - The query planner didn't like it when the "ORDER BY" referred to a
> column value instead of a static value, even when I believe it should
> know that the column value never changes. See this pseudo-query where
> we look-up the coordinates for 90210 once:

> EXPLAIN ANALYZE
> SELECT pets.pet_id,
> zipcodes.lon_lat <-> center.lon_lat AS radius
> FROM (SELECT lon_lat FROM zipcodes WHERE zipcode = '90210') AS
> center, pets
> JOIN shelters USING (shelter_id)
> JOIN zipcodes USING (zipcode)
> ORDER BY postal_codes.lon_lat <-> center.lon_lat limit 1000;

As phrased, that's a join condition, so there's no way that an index on
a single table can possibly satisfy it. You could probably convert it
to a sub-select though:

ORDER BY postal_codes.lon_lat <-> (SELECT lon_lat FROM zipcodes WHERE zipcode = '90210') limit 1000;

regards, tom lane